I have been wondering about this for a long time, and can't figure it out.
When I watch DP videos the pros manage to make the underpush long and parallel (i.e. in the direction of movement), which results in a relatively low cadence despite the speeds attained of 40+ kph. Now, when I work on my technique I am focusing on getting the proper lean on my underpush and on keeping the skates parallel to avoid too deep an arch and too much zig-zaking as a result. Yet I have big problems getting the latter right. I have experimented with my frame position, but still it does not cut it. It feels like I am anatomically not able to do the underpush and avoid too deep an arch/keep the skates parallel towards the direction I am travelling in.
Don't get me wrong, it's not dramatic and I don't skate lake a drunken sailor, yet it bugs me a lot.
How to work on it? How to improve?

I've been wondering and reading about this question and on this forum I have come across a potentially important tip: frame length. Actually, I've been wondering about the technical/gear implications on the angle at which I place my skates. Can it thus be that:
1) The longer the frame is the slower it will navigate/ carve --> maybe my current frame at 12,8" is not necessarily best for me and a longer one could help me address the problem?
2) the wheel profile / use. At higher speeds I feel often that the underpush leg skates from under me far too rapidly. It may just be the sensation and I certainly need to get someone to film me, but may this be a factor here?

3) the closed/open position of the frame (closed = aft part more to the outside, open = aft part more to the inside; it's relative to the front of the frame) with a closed position of the frame supporting a more parallel glide on the underpush? However, here is a problem, as I have recently moved the aft part of the frame inwards by extra 2mm and feel like it's what I needed and what prevents my left leg/ankle from bending in on the push (while extended outwards), so going for a closed position would bring me back to the starting point.

I've been watching this thread, hoping that one of the super competent skaters would provide their insights. I could blabber a bit about your question but I wouldn't consider myself a suitable resource.

Thank you guys for sharing your tips and thoughts. I am grateful to both of you, yet crave more information.
Maybe I am overthinking this, but this is one of my current main focus points on skates.
Chuck, both your points are valid, for sure. I have no problem aligining the knees, but I will be thinking about it during my next practice. Point 1 is absolutely key - maybe it will suffice to focus on trying to do it, but then again the key question seems to remain 'how to make it happen'?
I know there are drills for making the underpush a real push (one of them being the so called 'praying hands', and I've been doing this). Yet it seems to me I am arching/zig-zaging too much still which is counterproductive.
Anyway, if I figure out more, I will share with you.

I've been watching this thread, hoping that one of the super competent skaters would provide their insights. I could blabber a bit about your question but I wouldn't consider myself a suitable resource.

Come on, guys! Help us out here!

Since there isn't too much input, don't be shy and share whatever impressions/experience you have on this. Will be greatly appreciated!

Learn to slalom on 1 foot and how to maintain speed. You will be essentially doing a double push, but standing on only one leg.

The motions needed for acceleration are extremely similar.

There are many factors of double push strides that people overlook. One being that during the transition from underpush to traditional push the leg is accelerated outward, in the direction you are about to dump a large surge of power for a brief moment. Think of it like swinging a kid, you can always get a better push for them to go higher if you already have your arms in motion, even if your at touching their back while they are on the up swing, you are simply synchronizing yourself with the motions at play to be able to put power out at the most opportune time.

Another is that during the movement between under push and traditional push the leg straightens slightly and reaches forward, which also puts the foot in a better position right before you surge power into the stride. Which in turn makes the stride more effective. Since it wont be behind your hip during the peak power output if the stride is done well.

You get to roll your ankle over with the leg and blade acting as one , this is a huge advantage inlines have over quads, they gain a substantial extension of stride length in comparison to doing a DP stroke on quads.

When you begin the underpush part of the stride the toe digs in first to initiate an outward turn, as your foot start a to get under you the entire outside edge(blade of the foot) should have pressure on it and begins a small springy pulse to set your body and leg in motion, this is a pretty short moment, then the foot needs to come slightly forward, reaching forward as the knee starts to straighten, this keeps you from bobbing up and down, otherwise you are forced to change your ride height. It also prepares the foot to be in a much more prime location when your push strength is at its peak, so you can surge a large amount of force for a very brief moment to get maxium speed. The end of the cycle is your traditional stride countering the outward underpush portion of the DP stride. Kinda like bouncing on a trampoline, you set that one small bounce so you can really surge power into a much high bounce.

What you need to focus on is how smooth it feels, and did you get good speed for the amount of power you invested.

Practice 1 foot slalom, I promise it will help, the recovery foot will be behind you acting in a similar fashion, it will help correct your balances as well as assist in the stride, mainly how it will smooth the stride out, which results in better efficiency.

__________________
Home rink: Roll-A-Rama in Huntington Wv.
"Focus on form and speed is a byproduct, focus on speed and falling is a byproduct." - Matguy

... don't be shy and share whatever impressions/experience you have on this....

I only posted here to spur others to get involved when it appeared a great thread might die.

Simply put... I'm old, overweight, slow and clumsy. I cannot DP in the sense being discussed here. I use a far less pronounced version of the motion to get an extended duration primary push. However, having spent a 35 yr career in the understanding and practical application of physics, force vectors and weight shift I kind-of know how all the various elements come together. The trick is to come up with the best overall way to implement the various component elements so that the resulting "super-postion" (summary of all the various individual element's benefits and penalties) is helpful to a specific skater. (Well, DUH! Of course that is what should be done!) My point here is that sometimes we do things that feel good or look cool but ultimately can work against a specific skater. In addition to the primary elements, I believe a good DP also carefully manages the carving motion to reduce as much as practical the energy robbing wheel scrubbing.

I'm pretty sure you are still skating with "wide feet", aka your skates are not under you. Without seeing a video of your skating I can't be sure.
IMO when executed properly the dbl-push just works. You never need to think about the landing skate being straight.

So, let's go back to the basics on your form.

Drill- on your skate path, roll on one skate while doing all the push with the other. If you can do this for 100 yards or so on each skate that is a good start.

Item next: while doing single push on every recovery brush the skate against your ankle. This guarantees that your skate is under you.

When all this gets pretty automatic then you should start to see an improvement on your dbl-push.
If you can get some one to video your skating you can post it on YouTube so we can comment. Also, video will really help you.
There are 3 images of your skating:
The image you would like to look like; the image of what you think you look like; and the real one- the actual image of you skating.
Best of luck...
kaw

I've been able to DP for almost 20 years. I didn't even know it had a name when I was doing it. I just knew I could skate ridic fast compared to my friends, and that my stride was very different.

Recently I started teaching kids alot of moves at the local rink. And taught people how to DP, since a few years (5-6)ago I learned it was actually a thing, and I wasn't the only person who skated like that.

I noticed my timing in my quads vs my blades was not quite as good when I first started back on them., however one of the skills I teach kids often is 1 foot slalom. It is SOO freaking useful, and the more you do it , the better your edge to edge timing becomes.

Now I can put out some damn fast speeds on quads by making use of the DP technique, since it radically slows the stride cadence.

I even do a double push going backwards sometimes in the rink as part of my carving motions around people. I've learned to use that swing as I go around people to keep or build speed even. And ALL of that has come from 1 foot slalom practice.. LOTS of it. It has truly transformed my skillset(coupled with a few other things)

__________________
Home rink: Roll-A-Rama in Huntington Wv.
"Focus on form and speed is a byproduct, focus on speed and falling is a byproduct." - Matguy

First of all, sorry for a late reply, I've been away.
Thanks to all for all the contributions and useful tips. They are definitely helpful, and I am going to come back to exercising the one foot slalom.
However, I feel I need to apologiese for not being clear enough. Some of you clearly think that I am struggling with starting to double-push yet. This is fine, I wasn't clear enough and the reader is always right Especially Kentek felt almost sure I am skating with my feet wide. Well, despite a huge cleft between what I think I am doing and what I am doing in reality, I am sure I am already now doing the DP and I know the feeling, etc. I have been practising for the past months different elements of DP and doing specific exercise such as scooter, the praying hands drill, hang time, leaning exercise, putting the hip first, locking the ankle, recovery stroke, etc. I know I am doing the DP. Long story short: I am not a beginner.

What I was asking about was a question with which I am hoping to take my DP to the next level and to work on 'straightening' the underpush phase and make it less curvy to get the maximum out of each push, lower the cadence and 'milk' every move till the end

My considerations may be wrong and maybe I am overthinking/overanalysing. Dunno. Maybe the long strides and low cadence is the benefit of only bigger wheels like 110s and 125s? Maybe my current 100mm wheels are already worn out and I need to take new ones to slow down the transitions from the outside to the inside edge? There are simply many questions in my head that I am grappling with.

Soon enough, maybe next week I intend to finally make the transition to a hybrid Schankel frame that's been sitting in my drawer since December, waiting for me to get to a shape that will allow me to make an attempt at it. Maybe it's too early, but I won't know if I am not gonna try.

Some specific points:
- straighthening the knee in DP - yes! I've been doing an exercise for it since 2-3 weeks ago and it's such an overlooked part of DP. Literally, few coaches mention it. I observed and spotted it from a national team skater who was coaching us in a workshop. He did not make a point about it, only when I enquired did he mumble 'yes, maybe I am doing it...' Gee.

The double push takes a while to learn...maybe a couple years, or at least it did for me. When I first began trying to learn it, it didn't make sense to me. I could watch videos and visualize the technique (and it made sense), but when I actually tried to do it, nothing worked.

I'm a decent skater but am definitely not a coach, so I don't want to mislead you. I learned the double push by lots and lots of trial and error. But, for me, the most important part of the double push is where you land your skate. For example, if you land your skate too far underneath your body, it's hard to get any kind of underpush. Also, if your skate lands pointing outwards or even straight ahead, it's hard to initiate the inward "carve." So, for me, learning to land my skate slightly outside of my center line really helped. Also, learning to land my skate with my toe pointed slightly inwards helped a lot too. I also really focused on bringing my recovery skate behind my support leg to help force the inward push. This is not always the safest thing to do because I can't tell you how many times I "caught" my recovery skate on the back of my support skate (and fell). But, if you actually use your recovery leg and "kick back" behind your support leg, it can almost help create the underpush. I don't think this is "good technique," but it does help you learn to create an underpush. Today, I don't bring my recovery leg behind my support leg because I can generate the underpush "naturally" without such an exaggerated motion. I don't think it's safe to bring your recovery leg behind because sooner or later, you'll click the back of the your other skate (and fall). If you watch most of the pros, they don't have a super aggressive "recoveries" unless they are sprinting. Below is a video of Felix Rijhnen and notice his recovery leg basically stops when it reaches the point of his other skate. This is how you should do it, but again, when you are learning, you almost need that wasted motion of a huge recovery "kick" to help force the underpush.

You can watch all the videos in the world and the really good skaters will make it look like a piece of cake. And, it actually is that once you learn it. But, it's not natural and it takes a lot of muscle memory. You will have to get used to doing things that feel really wrong and really uncomfortable until one day they come together and make sense. When I first started, everything I did was over exaggerated, excessive motion (in many ways)...but those things helped create a bad double push. Today, everything I do is very subtle, very efficient and I think my double push is really good. So my point is that you will probably go from really big movements (that lead to fatigue), but once you start to master the form, you will slowly start to reduce the size of the movements because you won't need to exaggerate certain movements in order to make the technique work. Even things as simple as where you land your skate will start to be less exaggerated...I mentioned landing outside of your center line...this might start out as something crazy like 3 or 4 inches (off that line) and five years down the road be as little as an inch or less because you won't need as much "room" to create a good underpush.

Just my feedback...again, I'm not a coach and learned by doing a lot of things wrong (for a long time).

I was thinking about this some more last night and when I first started skating (and trying to learn the double push), I remember reading comments like, "The double push is virtually the same as the classic push with just an under push added in." While this may be semi-true, the double push isn't as easy as just doing the classic technique and quickly doing an under push when your skate is on the ground.

When you do the classic technique (like ice), all of your weight is "falling to the side" after you push. And, your landing skate has a tendency to want to point outwards as soon as it's on the ground. As you become more experienced, you can land your skate perfectly parallel to your direction of motion, but it very quickly starts to veer outwards as you begin the push.

With the double push, your weight is still falling to the side after the push, but your landing skate (leg) almost acts like a "brace"...meaning, as soon as you land, your weight keeps falling to the side, but your skate immediately starts to go the opposite direction (inwards). If you land your skate pointing slightly inwards, this is easier to do.

But, even my description doesn't make sense. Because if you just did the classic technique and focused really hard on pointing your skate inwards as it landed, you still wouldn't be able to do the double push. The double push requires a different motion, even though it looks identical to the classic push. You almost have to think..."fall, toe slightly in, land and catch (or use your leg to brace your fall), keep falling, under push, outer push." With the classic technique, it's more like "fall, toe straight ahead, land, ride your skate as long as you can before transferring your weight again." There is almost a slight pause when you land while doing the double push...you start falling, then land, catch (or brace) yourself, your skate starts to go inwards as you keep falling, which eventually forces your skate out of the under push and into the outer push.

I don't know...sorry that explanation isn't more clear. That's the best I can make sense of it. To me, it's a hard technique to teach because it seems so close to the classic form, but yet, is very different...but, your eyes can't quickly identify the differences (making it hard to train your body to do the right movements).

I think that an underpush comes almost naturally when you develop other aspects of your technique.
I find this is most evident when you look at a head-on shot of any elite skater.. the angle and placement of the foot on setdown is facilitated by everything else that is going on in the hips and the upper body. The ankle is straight but because of the lean they have going on in the upper body and where their center of mass is it means the left foot is pointing at 1o'clock and the right foot pointing at 11 o'clock when it is actually landing.

Thanks for all the advice, all is relevant and I have been taking all your remarks into account + experimenting with them.

I noticed one thing (maybe obvious, but still): the faster I go, the better my underpush and foot placement is - it's as if the angle of placement and the direction adjust automatically to the speed (brain is a fascinating thing). Secondly, I also tweaked my frame position further by moving it inwards a further 1-2mm. Small as this may be it changes the angle of the frame and helped smooth out the underpush's arc.
Thirdly, I am trying now to marry my hitherto technique with the forward drive of my shin in the second phase of the underpush (a little bit like straightening my support leg in the underpush). One of you guys mentioned it and I had seen this nuance last autumn too. I am not yet sure how much it adds to the speed and efficiency, but since I saw an elite skater do it, I reckon it's part of the elite technique.
I continue working on the one foot slalom (got some cones yesterday). I also check in my notes that it was a recommendation I took with me from a workshop I participated to last year. There, however, another variant of this exercise was recommended: going downhill (not too radical, just a small elevation) and going from one side to another while rolling on one leg. I guess the principle is the same.

After having been on ice for over 30 years, my brain didn't like the transfer to inline skates... I have 125 wheels on a 165 standard mount so the wheelbase was a lot longer than the effective "contact" area/length of my hockey skates.

As a result, I noticed two things when I made the switch to inline skating - 1) Immediately, it felt like the skate wanted to glide outward so I moved the frame outward so it felt more like an ice skate balance. 2) as a result of the longer contact area, it also felt like there was no manoeuvrability or potential for arcing each push.

I mention this as it might be relevant. After doing more and more inline skating, I've been deliberately placing my leading foot on the other side of my centre of gravity (i.e. right foot to the left and right foot to the left). Almost like the first part of a cross-over. This forces the use of the outside edge and, at least, gives you the option to use the underpush (maybe?). After doing this for a while, I then noticed myself doing almost like a double bounce. When the leading foot goes down, I would bend my knees into it and do a small bounce as my foot arcs round to the centreline and then outward for the main push. What I then also noticed was that I found myself wanting to put the frame back to where it was when it was new. I now wanted the skate to arc "outward" when I put the skate down.

This does however result in a zig-zig motion and, as mentioned earlier in the post, the pros seem to achieve a parallel skate motion whereas mine seems to be outward Vs all the time - as I would have done on ice.

This does however result in a zig-zig motion and, as mentioned earlier in the post, the pros seem to achieve a parallel skate motion whereas mine seems to be outward Vs all the time - as I would have done on ice.

This does however result in a zig-zig motion and, as mentioned earlier in the post, the pros seem to achieve a parallel skate motion whereas mine seems to be outward Vs all the time - as I would have done on ice.

The problem I want to pursue in this topic is the one you mention towards the end of your post: avoiding to much zig-zaging when doing the DP. It's relatively easy to imitate DP when doing a zig-zag, but this is not an effective technique. The video you posted is quite relevant and a great image of what the technique should be like: the guys feet zig-zag (doing the DP), but he stays perfectly in line. I've been wondering how much lateral motion is still OK for an effective DP - is it let's say 1,5m of upper body/head laterla motion, or less? When does one start zig-zaging and how to remedy this?

I have been focusing on this a lot recently and find it difficult to combine the following elements into one smooth technique/motion:
- underpush: outside edge parallel to the direction of motion;
- shoulder dip to amplify the underpush;
- prolonged glide with the fall initiated from the hip rather than the quadriceps.

It's complicated
Anyway, one question: I've been practising the one foot slalom and made good progress here. The question I have is: how far apart should the cones be spaced? Rather close to one another, or in eg. 2,5m distance?

I'm going to give you the simplest advise possible... Set down the foot in the direction of travel directly beneath you. You'll see that in the Swings vid - freeze frame or slow-mo the footage.

If you are stepping out side your shoulders or pointing your toes or foot in any other direction upon set-down there will be issues.

All that said, if you are someone with toes out or toed-in anatomical variations those will contribute to technique, and you may have to compensate for them. Have you posted a vid of your DP? maybe that will help us and others to give you better insight.

A really great way to get comfy on outside edges are to do slalom drills. It doesn't mater what skate you use, or with big or little wheels, just get used to carving on those edges.

adding:
Bart swings vid on DP. notice he does not leg whip- no need, he's using hip & upper body rotation to steer himself. skate set down & transfer are in parallel. if you were to dip his wheels in paint, you'd see he does zig-zag, though he's more tight and efficient, not over-exaggerated as some of the vids added to this thread. the arc is a component of dp, you cannot dp without that arc. the key is the transfer point and both skates parallel at this moment. if feet are pointing anywhere else at this moment, you're being inefficient. though, I will add there are some insanely crazy strong skaters out there that can compensate for technique deficiencies with strength.
Swings: https://www.youtube.com/watch?v=xTHvlyW6aBo